1. Field of the Invention
The present invention relates to a control device that drives a driven object, such as a work and tool, by two motors in a machine tool, etc.
2. Description of Related Art
In a machine tool etc., when it is not possible to accelerate and decelerate a driven object by one motor due to the size of the driven object of the motor being large, or when it is not possible to move a driven object in a stable state because backlash between the motor and the driven object is large, tandem control is performed in which one driven object is driven by two motors.
In such tandem control, when the coupling rigidity between two motors is high, there is a case where the drive forces of the two motors interfere with each other due to a slight synchronization error between the two motors and vibrations are produced. In order to suppress such vibrations, a control device having one processor (for example, digital signal processor (DSP)) that suppresses vibrations based on a speed value difference between two motors is proposed in, for example, Japanese Patent No. 3492583 (JP3492583B2).
However, there is a limit to the processing performance of one processor. For example, when the two motors are rotary servomotors having a plurality of stator windings for one rotor and one speed detector or when the two motors are two liner servomotors having a plurality of sliders for one magnet plate and one speed detector, processing of a plurality of motor drive units including current control, etc., is necessary for one motor, and therefore, it is not possible to control two motors by one processor. Consequently, there is a case where it is necessary to control two motors by two processors in order to suppress vibrations that may be produced by the tandem control of the two motors.